n-bit successive approximation register analog-to-digital converter and method for calibrating the same, receiver, base station and mobile device

ABSTRACT

A n-bit Successive Approximation Register Analog-to-Digital Converter, SAR ADC, is provided. The SAR ADC comprises a respective plurality of sampling cells for each bit of the n-bit of the SAR ADC. Each sampling cell comprises a capacitive element coupled to a cell output of the sampling cell in order to provide a cell output signal. Further, each sampling cell comprises a first cell input for receiving a first signal, and a first switch circuit capable of selectively coupling the first cell input to the capacitive element. Each cell additionally comprises a second cell input for receiving a second signal, and a third cell input for receiving a third signal. The third signal exhibits opposite polarity compared to the second signal. Each sampling cell comprises a second switch circuit capable of selectively coupling one of the second cell input and the third cell input to the capacitive element. The SAR ADC further comprises at least one comparator circuit coupled to the sampling cells. The at least one comparator circuit is configured to output a comparison signal based on the cell output signals of the sampling cells. Additionally, the SAR ADC comprises a calibration circuit configured to supply at least one respective control signal to the respective second switch circuit of the sampling cells for controlling the second switch circuits.

FIELD

The present disclosure relates to analog-to-digital conversion. Inparticular, examples relate to a n-bit Successive Approximation RegisterAnalog-to-Digital Converter (SAR ADC) and a method for calibrating thesame. Further examples relate to a receiver, a base station and a mobiledevice.

BACKGROUND

Split capacitor SAR ADC architectures have significant advantages froman analog implementation point of view. However, conventional splitcapacitor SAR ADCs are difficult to calibrate since the weight of theLeast Significant Bit (LSB) of the split capacitor SAR ADC is not afunction of the comparator decisions. As a consequence, it is difficultto estimate the LSB. However, the LSB weight is an important quantity.For example, if a split capacitor SAR ADC is used in a pipeline ADC, itis important to have an estimate for the LSB weight.

Hence, there may be a desired for an improved SAR ADC architecture.

BRIEF DESCRIPTION OF THE FIGURES

Some examples of apparatuses and/or methods will be described in thefollowing by way of example only, and with reference to the accompanyingfigures, in which

FIG. 1 illustrates an example of a n-bit SAR ADC;

FIG. 2 illustrates a first example of decision thresholds;

FIG. 3 illustrates a second example of decision thresholds;

FIG. 4 illustrates a third example of decision thresholds;

FIG. 5 illustrates another example of a n-bit SAR ADC;

FIG. 6 illustrates an example of a base station;

FIG. 7 illustrates an example of a mobile device; and

FIG. 8 illustrates a flowchart of an example of a method for calibratinga n-bit SAR ADC.

DETAILED DESCRIPTION

Various examples will now be described more fully with reference to theaccompanying drawings in which some examples are illustrated. In thefigures, the thicknesses of lines, layers and/or regions may beexaggerated for clarity.

Accordingly, while further examples are capable of various modificationsand alternative forms, some particular examples thereof are shown in thefigures and will subsequently be described in detail. However, thisdetailed description does not limit further examples to the particularforms described. Further examples may cover all modifications,equivalents, and alternatives falling within the scope of thedisclosure. Same or like numbers refer to like or similar elementsthroughout the description of the figures, which may be implementedidentically or in modified form when compared to one another whileproviding for the same or a similar functionality.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, the elements may bedirectly connected or coupled via one or more intervening elements. Iftwo elements A and B are combined using an “or”, this is to beunderstood to disclose all possible combinations, i.e. only A, only B aswell as A and B, if not explicitly or implicitly defined otherwise. Analternative wording for the same combinations is “at least one of A andB” or “A and/or B”. The same applies, mutatis mutandis, for combinationsof more than two Elements.

The terminology used herein for the purpose of describing particularexamples is not intended to be limiting for further examples. Whenever asingular form such as “a”, “an” and “the” is used and using only asingle element is neither explicitly nor implicitly defined as beingmandatory, further examples may also use plural elements to implementthe same functionality. Likewise, when a functionality is subsequentlydescribed as being implemented using multiple elements, further examplesmay implement the same functionality using a single element orprocessing entity. It will be further understood that the terms“comprises”, “comprising”, “includes” and/or “including”, when used,specify the presence of the stated features, integers, steps,operations, processes, acts, elements and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps, operations, processes, acts, elements, componentsand/or any group thereof.

Unless otherwise defined, all terms (including technical and scientificterms) are used herein in their ordinary meaning of the art to which theexamples belong.

FIG. 1 illustrates an example of a n-bit SAR ADC 100. In the example ofFIG. 1, the SAR ADC 100 is depicted as an n=4-bit ADC. Accordingly, theproposed SAR ADC architecture will be described with reference to a4-bit ADC. However, it is to be noted that the proposed architecture isnot limited to 4-bit SAR ADCs. In general, the proposed architecture maybe used for any number of bits n>1.

The SAR ADC 100 comprises a respective plurality of sampling cells foreach bit of the n=4-bit. That is, the SAR ADC 100 comprises a pluralityof sampling cells 110 for the 1^(st) Most Significant Bit (MSB) of the4-bit, a plurality of sampling cells 120 for the 2^(nd) MSB of the 4-bit(MSB-1), a plurality of sampling cells 130 for the 3^(rd) MSB of the4-bit (MSB-2), and a plurality of sampling cells 140 for the 4^(th) MSBof the 4-bit (i.e. the LSB). In the example of FIG. 1, each plurality ofsampling cells 110, . . . , 140 comprises two respective sampling cells.However, it is to be noted that the proposed architecture is not limitedto two sampling cells per bit. In general, any number m>1 of samplingcells may be used for each bit of the n-bit.

Further illustrated in FIG. 1 is a plurality of sampling cells 199 for adummy LSB that allow dummy switching during operation of the SAR ADC100. The sampling cells 199 for the dummy LSB are not needed forcalibration and will, hence, not described in detail in following. Insome examples, the sampling cells 199 for the dummy LSB may be omitted.

The individual sampling cells of the pluralities of sampling cells 110,. . . , 140 (and also the plurality of sampling cells 199 for the dummyLSB) are substantially identical. The structure of the sampling cellswill be exemplarily described in the following for the sampling cell110-1 of the plurality of sampling cells 110 for the 1^(st) MSB.

The sampling cell 110-1 comprises a capacitive element 111 coupled to acell output (node) 112 of the sampling cell 110-1 for providing a celloutput signal 113. Further, the sampling cell 110-1 comprises a firstcell input (node) 114 for receiving a first signal 101, and a firstswitch circuit 115 capable of selectively coupling the first cell input114 to the capacitive element 111. The sampling cell 110-1 additionallycomprises a second cell input (node) 116 for receiving a second signal102, and a third cell input (node) 117 for receiving a third signal 103.The sampling cell 110-1 comprises a second switch circuit 118 capable ofselectively coupling one of the second cell input 116 and the third cellinput 117 to the capacitive element 111. For example, the first switchcircuit 115 and the second switch circuit 118 may be implemented assemiconductor switches (e.g. comprising one or more transistors).

The first signal 101 is a calibration signal, the second signal 102 is afirst reference signal, and the third signal 103 is a second referencesignal. The third signal 103 exhibits opposite polarity compared to thesecond signal 102.

In the example of FIG. 1, the first cell input 114 of the sampling cell110-1 is a cell input of the sampling cell used for receiving an inputsignal to be digitized during non-calibration operation of the SAR ADC(i.e. when the SAR ADC is not calibrated). In other words, SAR ADC 100uses the regular cell input of the sampling cell 110-1 for receiving(inputting, injecting) the calibration signal to the sampling cell110-1. In other examples, the first cell input 114 may be a dedicatedcell input used only for receiving calibration signals.

The SAR ADC 100 is a split capacitor SAR ADC.

The capacitive elements of a respective one of the pluralities ofsampling cells 110, . . . , 140 for the individual bits of the n=4-bitexhibit the same capacitance. As indicated in FIG. 1, each capacitiveelement of the plurality of sampling cells 110 for the 1^(st) MSBexhibits the capacitance α³·C_(U)/2 (C_(U) denotes a unit capacitance),each capacitive element of the plurality of sampling cells 120 for the2^(nd) MSB exhibits the capacitance α²·C_(U)/2, each capacitive elementof the plurality of sampling cells 130 for the 3^(rd) MSB exhibits thecapacitance α¹·C_(U)/2, and each capacitive element of the plurality ofsampling cells 140 for the 4^(th) MSB exhibits the capacitanceα⁰·C_(U)/2. In other words, each capacitive element of a respectiveplurality of sampling cells for a bit of the n=4-bit exhibits abit-specific capacitance.

The capacitive elements of a respective one of the pluralities ofsampling cells 110, . . . , 140 for the individual bits of the n=4-bitexhibit a respective capacitance which corresponds to the significanceof the respective bit. That is, the capacitance α³·C_(U)/2 of thecapacitive elements of the plurality of sampling cells 110 for the1^(st) MSB corresponds to the significance of the 1^(st) MSB, thecapacitance α²·C_(U)/2 of the capacitive elements of the plurality ofsampling cells 120 for the 2^(nd) MSB corresponds to the significance ofthe 2^(nd) MSB, etc.

Therefore, the capacitive elements of different ones of the pluralitiesof sampling cells 110, . . . , 140 for the individual bits of then=4-bit exhibit different capacitances. The capacitance α³·C_(U)/2 ofthe plurality of sampling cells 110 for the 1^(st) MSB is different fromthe capacitance α²·C_(U)/2 of the capacitive elements of the pluralityof sampling cells 120 for the 2^(nd) MSB, the capacitance α²·C_(U)/2 ofthe capacitive elements of the plurality of sampling cells 120 for the2^(nd) MSB is different from the capacitance α¹·C_(U)/2 of thecapacitive elements of the plurality of sampling cells 130 for the3^(rd) MSB, etc.

The SAR ADC 100 further comprises at least one comparator circuitcoupled to (the cell outputs of) the sampling cells of the pluralitiesof sampling cells 110, . . . , 140. In the example of FIG. 1, fourcomparator circuit 150-1, . . . , 150-4 are illustrated as the SAR ADC100 comprises a respective comparator circuit for each of the n=4-bit.In alternative examples, a single (i.e. only one) comparator circuit maybe used for all of the n=4-bit. The comparator circuits 150-1, . . . ,150-4 are configured to output a respective comparison signal 151-1, . .. , 151-4 based on the cell output signals of the sampling cells of thepluralities of sampling cells 110, . . . , 140. Accordingly, if a singlecomparator circuit is used, the comparator circuit is configured tooutput a single comparison signal based on the cell output signals ofthe sampling cells.

In the example of FIG. 1, the cell output signals of the sampling cellsof the pluralities of sampling cells 110, . . . , 140 are combined andsupplied to a respective first comparator input (node) of each of thecomparator circuits 150-1, . . . , 150-4. Further, a comparisonreference signal 152 is input to a respective second comparator input(node) of each of the comparator circuits 150-1, . . . , 150-4. Each ofthe comparator circuits 150-1, . . . , 150-4 is configured to comparethe comparison reference signal 152 to the combined cell output signalsof the sampling cells of the pluralities of sampling cells 110, . . . ,140, and to generate the respective comparison signal 151-1, . . . ,151-4 based on the comparison of the comparison reference signal 152 tothe combined cell output signals of the sampling cells of thepluralities of sampling cells 110, . . . , 140. For example, dependingon which of the comparison reference signal 152 and the combined celloutput signals of the sampling cells of the pluralities of samplingcells 110, . . . , 140 exhibits the higher signal level, the respectivecomparator circuit 150-1, . . . , 150-4 may adjust the signal level ofthe respective comparison signal 151-1, . . . , 151-4 (e.g. high or lowdepending on which of the signals input to the respective comparatorcircuit exhibits the higher/lower signal level).

The SAR ADC 100 additionally comprises a calibration circuit 160configured to supply at least one respective control signal to therespective second switch circuit of the sampling cells of thepluralities of sampling cells 110, . . . , 140 for controlling thesecond switch circuits. In the example of FIG. 1, the calibrationcircuit 160 supplies two respective control signals to the respectivesecond switch circuit of each of the sampling cells. For example, thecalibration circuit 160 supplies the two control signals 161-1 and 162-1to the second switch circuit 118 of the sampling cell 110-1. However, itis to be noted that in alternative examples more or less control signalsmay be supplied to the respective second switch circuit of the samplingcells of the pluralities of sampling cells 110, . . . , 140 forcontrolling the second switch circuits.

In the example of FIG. 1, the calibration circuit 160 comprises arespective logic circuit 163-1, . . . , 163-4 for each of the n=4-bit.For example, the logic circuit 163-1, . . . , 163-4 may implement therespective SAR logic for each of the n=4-bit. However, it is to be notedthat in alternative examples, a single (i.e. only one) or less than nlogic circuits implementing the SAR logic may be used. Furtherillustrated is a logic circuit 198 configured to supply control signalsto the second switch circuits of the plurality of sampling cells 199 forcontrolling the second switch circuits of the plurality of samplingcells 199 for the dummy LSB.

For calibration, the calibration circuit 160 may be configured to supplythe respective control signal(s) to the respective second switch circuitof the sampling cells of the pluralities of sampling cells 110, . . . ,140 in order to adjust a decision threshold for the comparator circuits150-1, . . . , 150-4 during calibration.

The SAR ADC 100 may enable facilitated calibration. In particular, theSAR ADC 100 may enable facilitated estimation of the weight of the LSB(e.g. the 4^(th) MSB in the example of FIG. 1). This will become clearerfrom the following description of the proposed calibration scheme.

For a n-bit SAR ADC, the proposed calibration scheme comprises n+1calibration measurements in order to determine the respective weight ofthe sampling cells for each of the n-bit. For the 4-bit SAR ADC 100illustrated in FIG. 1, the calibration scheme, hence, comprises fivecalibration measurements.

For the first calibration measurement, the calibration circuit 160 isconfigured to control the second switch circuits of one half of thesampling cells for each bit of the n=4-bit to couple the respectivesecond cell input to the respective capacitive element, and to controlthe second switch circuits of the other half of the sampling cells foreach bit of the n=4-bit to couple the respective third cell input to therespective capacitive element. In other words, for each of the n=4-bit,one sampling cell is controlled to couple its second cell input to itscapacitive element, and the other sampling cell is controlled to coupleits third cell input to its capacitive element. For example, for the1^(st) MSB, the sampling cell 110-1 may be controlled to couple itssecond cell input to its capacitive element, and the sampling cell 110-2may be controlled to couple its second cell input to its capacitiveelement. The sampling cells for the other bits may be controlledanalogously.

Coupling one half of each bit to the first reference signal and otherhalf to the other reference signal sets the decision threshold for thecomparator circuits 150-1, . . . , 150-4 initially to zero. This isillustrated in FIG. 2, which shows an exemplary decision tree 200 of theSAR ADC 100. The initially set decision threshold 201 is zero. Thedecisions of the comparator circuits 150-1, . . . , 150-4 based on thedecision threshold 201 do not contain any information about the weightof the 1^(st) MSB. During the first calibration measurement, thecalibration circuit 160 is configured to control the first switchcircuit of each sampling cell of the pluralities of sampling cells 110,. . . , 140 to decouple the respective first cell input from therespective capacitive element.

Further, i-th calibration measurements (1<i<n+1) are performed fordetermining the weights of the n−1 MSBs. For the n=4-bit SAR ADC 100illustrated in FIG. 1, the calibration scheme, hence, comprises n−1=3further calibration measurements (i.e. calibration measurements 2 to 4).

For each of the i-th calibration measurements, the calibration circuit160 is configured to respectively control the second switch circuits ofthe sampling cells for the i−1st MSB of the n=4-bit to sequentiallycouple the respective second cell input and the respective third cellinput to the respective capacitive element. Further, if i>2, thecalibration circuit 160 is configured to respectively control the secondswitch circuits of the sampling cells for the bits up to the i−2nd MSBto couple a selected one of the respective second cell input and therespective third cell input to the respective capacitive element.Additionally, the calibration circuit 160 is configured to respectivelycontrol the second switch circuits of one half of the sampling cells foreach of the i-th to n-th MSBs to couple the respective second cell inputto the respective capacitive element, and to respectively control thesecond switch circuits of the other half of the sampling cells for eachof the i-th to n-th MSBs to couple the respective third cell input tothe respective capacitive element.

Further, for each of the i-th calibration measurements, the calibrationcircuit 160 is configured to control the respective first switch circuitof the sampling cells for each bit of the n=4-bit to couple therespective first cell input to the respective capacitive element duringcalibration. The calibration signal exhibits an increasing or decreasingsignal level over time. In other words, the calibration signal allows tosweep a DC value into the SAR ADC 100.

For the 2^(nd) calibration measurement, the calibration circuit 160 inthe example of FIG. 1 is configured to respectively control the secondswitch circuits of the sampling cells 110-1 and 110-2 for the 1^(st) MSBto sequentially couple the respective second cell input and therespective third cell input to the respective capacitive element. Forexample, the second switch circuits of the sampling cells 110-1 and110-2 for the 1^(st) MSB may be controlled to first couple (only,exclusively) the respective second cell input to the respectivecapacitive element and then (only, exclusively) the respective thirdcell input, or vice versa. Further, the calibration circuit 160 isconfigured to respectively control the second switch circuits of onehalf of the sampling cells for each of the 2^(nd) to 4^(th) MSBs tocouple the respective second cell input to the respective capacitiveelement, and to respectively control the second switch circuits of theother half of the sampling cells for each of the 2^(nd) to 4^(th) MSBsto couple the respective third cell input to the respective capacitiveelement. For example, the second switch circuits of the sampling cells120-1, 130-1 and 140-1 may be controlled to couple the respective secondcell input to the respective capacitive element, and the sampling cells120-2, 130-3 and 140-2 may be controlled to couple the respective thirdcell input to the respective capacitive element.

For the 2^(nd) calibration measurement, the decision threshold for thecomparator circuits 150-1, . . . , 150-4 is therefore sequentially setto the decision thresholds 202 and 203, which convey information aboutthe weight w₃ of the sampling cells 110-1 and 110-2 of the 1^(st) MSB.In particular, the decision threshold 202 corresponds to +w₃ and thedecision threshold 203 corresponds to −w₃. Since the calibration signalwith increasing or decreasing signal level is input during the 2^(nd)calibration measurement, the threshold crossings around −w₃ and +w₃ canbe detected in the comparison signals 151-1, . . . , 151-4 of thecomparator circuits 150-1, . . . , 150-4. Accordingly, two measurementsvalue −w₃ and +w₃ for the weight w₃ of the sampling cells 110-1 and110-2 of the 1^(st) MSB are obtained. By subtracting the measurementsvalue −w₃ and +w₃ from each other, an estimate for the weight w₃ of thesampling cells 110-1 and 110-2 of the 1^(st) MSB may be obtained by thecalibration circuit 160.

For the 3^(rd) calibration measurement, the calibration circuit 160 inthe example of FIG. 1 is configured to respectively control the secondswitch circuits of the sampling cells 120-1 and 120-2 for the 2^(nd) MSBto sequentially couple the respective second cell input and therespective third cell input to the respective capacitive element. Forexample, the second switch circuits of the sampling cells 120-1 and120-2 for the 2^(nd) MSB may be controlled to first couple (only,exclusively) the respective second cell input to the respectivecapacitive element and then (only, exclusively) the respective thirdcell input, or vice versa.

Further, since i=3>2, the calibration circuit 160 is configured torespectively control the second switch circuits of the sampling cells110-1 and 110-2 for the 1^(st) MSB to couple a selected one of therespective second cell input and the respective third cell input to therespective capacitive element. The calibration circuit 160 is configuredto select the selected one of the respective second cell input and therespective third cell input based on the comparison signals 151-1, . . ., 151-4 for the 1^(st) calibration measurement. For example, if thesignal amplitude of the reference signal 152 is lower than the combinedcell output signals of the sampling cells of the pluralities of samplingcells 110, . . . , 140 in the 1^(st) calibration measurement, therespective second cell input may be selected as the selected one of therespective second cell input and the respective third cell input, orvice versa. In the following it will be assumed that the respectivesecond cell input is selected as the selected one of the respectivesecond cell input and the respective third cell input.

Further, the calibration circuit 160 is configured to respectivelycontrol the second switch circuits of one half of the sampling cells foreach of the 3^(rd) to 4^(th) MSBs to couple the respective second cellinput to the respective capacitive element, and to respectively controlthe second switch circuits of the other half of the sampling cells foreach of the 3^(rd) to 4^(th) MSBs to couple the respective third cellinput to the respective capacitive element. For example, the secondswitch circuits of the sampling cells 130-1 and 140-1 may be controlledto couple the respective second cell input to the respective capacitiveelement, and the sampling cells 130-2 and 140-2 may be controlled tocouple the respective third cell input to the respective capacitiveelement.

For the 3^(rd) calibration measurement, the decision threshold for thecomparator circuits 150-1, . . . , 150-4 is therefore sequentially setto the decision thresholds 204 and 205, which convey information aboutthe weight w₂ of the sampling cells 120-1 and 120-2 of the 2^(nd) MSB.In particular, the decision threshold 204 corresponds to w₃+w₂ and thedecision threshold 205 corresponds to w₃−w₂. Since the calibrationsignal with increasing or decreasing signal level is input during the3^(rd) calibration measurement, the threshold crossings around w₃−w₂ andw₃+w₂ can be detected in the comparison signals 151-1, . . . , 151-4 ofthe comparator circuits 150-1, . . . , 150-4. Accordingly, twomeasurements value w₃−w₂ and w₃+w₂ for the weight w₂ of the samplingcells 120-1 and 120-2 of the 2^(nd) MSB are obtained. By subtracting themeasurements value w₃−w₂ and w₃+w₂ from each other, an estimate for theweight w₂ of the sampling cells 120-1 and 120-2 of the 2^(nd) MSB may beobtained by the calibration circuit 160. In other words, a DC value isswept into the SAR ADC until the threshold crossings around w₃−w₂ andw₃+w₂ are detected. Subtracting these values gives an estimate for w₂.

For the 4^(th) calibration measurement, the calibration circuit 160 inthe example of FIG. 1 is configured to respectively control the secondswitch circuits of the sampling cells 130-1 and 130-2 for the 3^(rd) MSBto sequentially couple the respective second cell input and therespective third cell input to the respective capacitive element. Forexample, the second switch circuits of the sampling cells 130-1 and130-2 for the 3^(rd) MSB may be controlled to first couple (only,exclusively) the respective second cell input to the respectivecapacitive element and then (only, exclusively) the respective thirdcell input, or vice versa.

Further, since i=4>2, the calibration circuit 160 is configured torespectively control the second switch circuits of the sampling cells110-1 and 110-2 for the 1^(st) MSB and the sampling cells 120-1 and120-2 for the 2^(nd) MSB to couple the selected one of the respectivesecond cell input and the respective third cell input to the respectivecapacitive element.

Further, the calibration circuit 160 is configured to respectivelycontrol the second switch circuits of one half of the sampling cells forthe 4^(th) MSBs to couple the respective second cell input to therespective capacitive element, and to respectively control the secondswitch circuits of the other half of the sampling cells for the 4^(th)MSBs to couple the respective third cell input to the respectivecapacitive element. For example, the second switch circuit of thesampling cell 140-1 may be controlled to couple its second cell input toits capacitive element, and the sampling cell 140-2 may be controlled tocouple its third cell input to its capacitive element.

For the 4^(th) calibration measurement, the decision threshold for thecomparator circuits 150-1, . . . , 150-4 is therefore sequentially setto the decision thresholds 206 and 207, which convey information aboutthe weight w₁ of the sampling cells 130-1 and 130-2 of the 3^(rd) MSB.In particular, the decision threshold 206 corresponds to w₃+w₂+w₁ andthe decision threshold 207 corresponds to w₃+w₂−w₁. Since thecalibration signal with increasing or decreasing signal level is inputduring the 4^(th) calibration measurement, the threshold crossingsaround w₃+w₂−w₁ and w₃+w₂+w₁ can be detected in the comparison signals151-1, . . . , 151-4 of the comparator circuits 150-1, . . . , 150-4.Accordingly, two measurements value w₃+w₂−w₁ and w₃+w₂+w₁ for the weightw₁ of the sampling cells 130-1 and 130-2 of the 3^(rd) MSB are obtained.By subtracting the measurements value w₃+w₂−w₁ and w₃+w₂+w₁ from eachother, an estimate for the weight w₁ of the sampling cells 130-1 and130-2 of the 3^(rd) MSB may be obtained by the calibration circuit 160.In other words, a DC value is swept into the SAR ADC until the thresholdcrossings around w₃+w₂−w₁ and w₃+w₂+w₁ are detected. Subtracting thesevalues gives an estimate for w₁.

As described above, the calibration circuit 160 is configured todetermine a respective value for the weight of the sampling cells forthe i−1st MSB based on the comparison signal(s) for the i-th calibrationmeasurement.

The last determined threshold is a linear combination of w₃, w₂ and w₁,but not of the weight w₀ of the n-th MSB (i.e. the LSB) of the SAR ADC100. In order to determine the weight w₀ of the n-th MSB, an n+1stcalibration measurement.

For the n+1st calibration measurement, the calibration circuit 160 isconfigured to control the second switch circuits of the sampling cellsfor the bits up to the n−1^(st) MSB to couple the selected one of therespective second cell input and the respective third cell input to therespective capacitive element. Further, the calibration circuit 160 isconfigured to control the second switch circuits of the sampling cellsfor the n-th MSB (i.e. the LSB) to sequentially couple the respectivesecond cell input and the respective third cell input to the respectivecapacitive element.

For the n+1st calibration measurement, the calibration circuit 160 isagain configured to control the respective first switch circuit of thesampling cells for each bit of the n=4-bit to couple the respectivefirst cell input to the respective capacitive element duringcalibration.

In the above example, the n+1st calibration measurement is the 5^(th)calibration measurement. For the 5^(th) calibration measurement, thecalibration circuit 160 in the example of FIG. 1 is configured torespectively control the second switch circuits of the sampling cells110-1 and 110-2 for the 1^(st) MSB, the sampling cells 120-1 and 120-2for the 2^(nd) MSB and the sampling cells 130-1 and 130-2 for the 3^(rd)MSB to couple the selected one of the respective second cell input andthe respective third cell input to the respective capacitive element.

Additionally, the calibration circuit 160 is configured to respectivelycontrol the second switch circuits of the sampling cells 140-1 and 140-2for the 4^(th) MSB to sequentially couple the respective second cellinput and the respective third cell input to the respective capacitiveelement. For example, the second switch circuits of the sampling cells140-1 and 140-2 for the 4^(th) MSB may be controlled to first couple(only, exclusively) the respective second cell input to the respectivecapacitive element and then (only, exclusively) the respective thirdcell input, or vice versa. Initializing the SAR ADC LSB may be done veryeasy: One gate in the LSB feedback path may be added or replaced. Sincethe LSB uses a small capacitor, the required strength of the gates inthis path is small and the power increase to maintain low latency issmall.

For the 5^(th) calibration measurement, the decision threshold for thecomparator circuits 150-1, . . . , 150-4 is therefore sequentially setto the decision thresholds 208 and 209, which convey information aboutthe weight w₀ of the sampling cells 140-1 and 140-2 of the 4^(th) MSB.The decision threshold 208 is illustrated in FIG. 3. FIG. 3 illustratesa modified decision tree 300 assuming that the sampling cells 140-1 and140-2 for the 4^(th) MSB couple the respective second cell input to therespective capacitive element. The decision threshold 209 is illustratedin FIG. 4. FIG. 4 illustrates a modified decision tree 400 assuming thatthe sampling cells 140-1 and 140-2 for the 4^(th) MSB couple therespective third cell input to the respective capacitive element.

As can be seen from FIGS. 3 and 4, the decision threshold 208corresponds to w₃+w₂+w₁+w₀ and the decision threshold 209 corresponds tow₃+w₂+w₁−w₀. Since the calibration signal with increasing or decreasingsignal level is input during the 5^(th) calibration measurement, thethreshold crossings around w₃+w₂+w₁−w₀ and w₃+w₂+w₁+w₀ can be detectedin the comparison signals 151-1, . . . , 151-4 of the comparatorcircuits 150-1, . . . , 150-4. Accordingly, two measurements valuew₃+w₂+w₁−w₀ and w₃+w₂+w₁+w₀ for the weight w₀ of the sampling cells140-1 and 140-2 of the 4^(th) MSB are obtained. By subtracting themeasurements value w₃+w₂+w₁−w₀ and w₃+w₂+w₁+w₀ from each other, anestimate for the weight w₀ of the sampling cells 140-1 and 140-2 of the4^(th) MSB may be obtained by the calibration circuit 160. In otherwords, a DC value is swept into the SAR ADC until the thresholdcrossings around w₃±w₂±w₁−w₀ and w₃+w₂+w₁+w₀ are detected. Subtractingthese values gives an estimate for w₀.

As described above, the calibration circuit 160 is configured todetermine a value for the weight of the sampling cells for the n-th MSBbased on the comparison signal(s) for the n+1st calibration measurement.

Using the proposed calibration scheme, weights for all n-bits of the SARADC 100 may be estimated. In particular, the weight w₀ for the LSB ofthe SAR ADC 100 may be estimated.

The above described SAR ADC 100 is a single-ended ADC. It is to be notedthat the above described calibration scheme may as well be used for adifferential SAR ADC. An example of a differential n-bit SAR ADC 500 isillustrated in FIG. 5. In the example of FIG. 5, the SAR ADC 500 isdepicted as an n=4-bit ADC.

Like the SAR ADC 100, the SAR ADC 500 comprises a respective pluralityof sampling cells 510, 520, 530, 540 for each bit of n=4-bit. Further,the SAR ADC 500 comprises at least one comparator circuit 550 coupled to(the cell outputs of) the sampling cells of the pluralities of samplingcells 510, . . . , 540. Accordingly, the at least one comparator circuit550 is configured to output a comparison signal 551 based on the celloutput signals of the sampling cells of the pluralities of samplingcells 510, . . . , 540. A residue amplifier 590 is coupled between thesampling cells of the pluralities of sampling cells 510, . . . , 540 andthe at least one comparator circuit 550 in order to amplify the celloutput signals of the sampling cells.

The calibration circuit of the SAR ADC 500 is not illustrated in FIG. 5for reasons of simplicity. However, as described above for the SAR ADC100, the calibration circuit of the SAR ADC 500 receives the comparisonsignal 551 of the at least one comparator circuit 550 and controls theswitching circuits of the sampling cells.

The structure of the SAR ADC 500 is, hence substantially similar to thatof the SAR ADC 100 described above. Therefore, the SAR ADC 500 may becalibrated as described above.

Merely the structure of the sampling cells of the SAR ADC 500 isdifferent from the structure of the sampling cells of the SAR ADC 100described above. The difference between the sampling cells will bedescribed in the following by comparing the sampling cell 110-1 of theSAR ADC 100 with the sampling cell 510-1 of the SAR ADC 500.

In the sampling cell 110-1, the first cell input 114 is used forreceiving the first signal (i.e. the calibration signal) duringcalibration and for receiving an input signal (i.e. a fifth signal) tobe digitized during non-calibration operation of the SAR ADC 100. Thesampling cell 510-1 comprises an additional fourth cell input (node) 514for receiving the input signal to be digitized during non-calibrationoperation of the SAR ADC 500. Additionally, the sampling cell 510-1comprises a third switch circuit 509 capable of selectively coupling thefourth cell input 514 to the capacitive element 111 of the sampling cell510-1 based on a clock signal Φ₁ in order to sample the input signal.

Further, the sampling cell 510-1 comprises an additional fifth cellinput 519 for receiving a fourth signal. The fourth is anothercalibration signal and exhibits opposite polarity compared to the firstsignal. The first switch circuit 115 is capable of selectively couplingone of the first cell input 114 and the fifth cell input 519 to thecapacitive element 111 in the example of FIG. 5. The calibration circuitof the SAR ADC 500 is accordingly configured to control the first switchcircuit 115 to couple a selected one of the first cell input 114 and thefifth cell input 519 to the capacitive element during calibration (e.g.for the r-th calibration measurements with r>1). Accordingly, the fifthsignal may be used for calibration instead of the first signal.Alternatively, the calibration may be performed using one of the firstsignal and the fifth signal, and subsequently using the other of thefirst signal and the fifth signal.

It is to be noted that in other examples, the differential SAR ADC 500may alternatively use the sampling cell structure as described above forthe SAR ADC 100. Similarly, the SAR ADC 100 may use the sampling cellstructure described for the SAR ADC 500.

An example of an implementation using a n-bit SAR ADC according to oneor more aspects of the architecture described above in connection withFIGS. 1 to 5 or one or more examples described above in connection withFIGS. 1 to 5 is illustrated in FIG. 6. FIG. 6 schematically illustratesan example of a radio base station 600 (e.g. for a femtocell, apicocell, a microcell or a macrocell) comprising a n-bit SAR ADC 620 asproposed.

The n-bit SAR ADC 620 is part of a receiver 610. The receiver 610additionally comprises a signal generation circuit 630 coupled to then-bit SAR ADC 620. The signal generation circuit 630 is configured togenerate the first signal (e.g. exhibiting an increasing or decreasingsignal level over time) for calibrating the n-bit SAR ADC 620.

The receiver 610 is coupled to an antenna element 650 of the basestation 600 (either directly or indirectly via one or more intermediateelements such as a filter or a Low Noise Amplifier, LNA). The n-bit SARADC 620 is coupled to the antenna element 650 for digitizing a radiofrequency receive signal received by the antenna element 650.

Further, the base station 600 comprises a transmitter 640 configured togenerate a radio frequency transmit signal. The transmitter 640 may usethe antenna element 650 or another antenna element (not illustrated) ofthe base station 600 for radiating the radio frequency transmit signalto the environment.

To this end, a base station with a SAR ADC enabling facilitatedcalibration may be provided.

The base station 600 may comprise further elements such as, e.g., abaseband processor, an application processor, memory, a networkcontroller, a user interface, power management circuitry, a satellitenavigation receiver, a network interface controller or power teecircuitry.

In some aspects, the application processor may include one or moreCentral Processing Unit CPU cores and one or more of cache memory, aLow-DropOut (LDO) voltage regulator, interrupt controllers, serialinterfaces such as Serial Peripheral Interface (SPI), Inter-IntegratedCircuit (I²C) or universal programmable serial interface module, RealTime Clock (RTC), timer-counters including interval and watchdog timers,general purpose Input-Output (IO), memory card controllers such asSecure Digital (SD)/MultiMedia Card (MMC) or similar, Universal SerialBus (USB) interfaces, Mobile Industry Processor Interface Alliance(MIPI) interfaces and Joint Test Access Group (JTAG) test access ports.

In some aspects, the baseband processor may be implemented, for example,as a solder-down substrate including one or more integrated circuits, asingle packaged integrated circuit soldered to a main circuit board or amulti-chip module containing two or more integrated circuits.

In some aspects, the memory may include one or more of volatile memoryincluding Dynamic Random Access Memory (DRAM) and/or Synchronous DynamicRandom Access Memory (SDRAM), and Non-Volatile Memory (NVM) includinghigh-speed electrically erasable memory (commonly referred to as Flashmemory), Phase change Random Access Memory (PRAM), MagnetoresistiveRandom Access Memory (MRAM) and/or a three-dimensional crosspoint (3DXPoint) memory. The memory may be implemented as one or more of solderdown packaged integrated circuits, socketed memory modules and plug-inmemory cards.

In some aspects, the power management integrated circuitry may includeone or more of voltage regulators, surge protectors, power alarmdetection circuitry and one or more backup power sources such as abattery or capacitor. Power alarm detection circuitry may detect one ormore of brown out (under-voltage) and surge (over-voltage) conditions.

In some aspects, the power tee circuitry may provide for electricalpower drawn from a network cable to provide both power supply and dataconnectivity to the base station using a single cable.

In some aspects, the network controller may provide connectivity to anetwork using a standard network interface protocol such as Ethernet.Network connectivity may be provided using a physical connection whichis one of electrical (commonly referred to as copper interconnect),optical or wireless.

In some aspects, the satellite navigation receiver module may includecircuitry to receive and decode signals transmitted by one or morenavigation satellite constellations such as the Global PositioningSystem (GPS), GLObalnaya NAvigatSionnaya Sputnikovaya Sistema (GLONASS),Galileo and/or BeiDou. The receiver may provide data to the applicationprocessor which may include one or more of position data or time data.The application processor may use time data to synchronize operationswith other radio base stations.

In some aspects, the user interface may include one or more of physicalor virtual buttons, such as a reset button, one or more indicators suchas Light Emitting Diodes (LEDs) and a display screen.

Another example of an implementation using a n-bit SAR ADC according toone or more aspects of the architecture described above in connectionwith FIGS. 1 to 5 or one or more examples described above in connectionwith FIGS. 1 to 5 is illustrated in FIG. 7. FIG. 7 schematicallyillustrates an example of a mobile device 700 (e.g. mobile phone,smartphone, tablet-computer, or laptop) comprising a n-bit SAR ADC 720as proposed.

The n-bit SAR ADC 720 is part of a receiver 710. The receiver 710additionally comprises a signal generation circuit 730 coupled to then-bit SAR ADC 620. The signal generation circuit 730 is configured togenerate the first signal (e.g. exhibiting an increasing or decreasingsignal level over time) for calibrating the n-bit SAR ADC 720.

The receiver 710 is coupled to an antenna element 750 of the mobiledevice 700 (either directly or indirectly via one or more intermediateelements such as a filter or an LNA). The n-bit SAR ADC 720 is coupledto the antenna element 750 for digitizing a radio frequency receivesignal received by the antenna element 750.

Further, the mobile device 700 comprises a transmitter 740 configured togenerate a radio frequency transmit signal. The transmitter 740 may usethe antenna element 750 or another antenna element (not illustrated) ofthe mobile device 700 for radiating the radio frequency transmit signalto the environment.

To this end, a mobile device with a SAR ADC enabling facilitatedcalibration may be provided.

The mobile device 700 may comprise further elements such as, e.g., abaseband processor, memory, a connectivity module, a Near FieldCommunication (NFC) controller, an audio driver, a camera driver, atouch screen, a display driver, sensors, removable memory, a powermanagement integrated circuit or a smart battery.

In some aspects, the application processor may include, for example, oneor more CPU cores and one or more of cache memory, LDO regulators,interrupt controllers, serial interfaces such as SPI, I²C or universalprogrammable serial interface module, RTC, timer-counters includinginterval and watchdog timers, general purpose input-output (TO), memorycard controllers such as SD/MMC or similar, USB interfaces, MIPIinterfaces and JTAG test access ports.

In some aspects, the baseband module may be implemented, for example, asa solder-down substrate including one or more integrated circuits, asingle packaged integrated circuit soldered to a main circuit board,and/or a multi-chip module containing two or more integrated circuits.

The wireless communication circuits using a SAR ADC according to theproposed architecture or one or more of the examples described above maybe configured to operate according to one of the 3GPP-standardizedmobile communication networks or systems. The mobile or wirelesscommunication system may correspond to, for example, a 5G NR, aLong-Term Evolution (LTE), an LTE-Advanced (LTE-A), High Speed PacketAccess (HSPA), a Universal Mobile Telecommunication System (UMTS) or aUMTS Terrestrial Radio Access Network (UTRAN), an evolved-UTRAN(e-UTRAN), a Global System for Mobile communication (GSM), an EnhancedData rates for GSM Evolution (EDGE) network, or a GSM/EDGE Radio AccessNetwork (GERAN). Alternatively, the wireless communication circuits maybe configured to operate according to mobile communication networks withdifferent standards, for example, a Worldwide Inter-operability forMicrowave Access (WIMAX) network IEEE 802.16 or Wireless Local AreaNetwork (WLAN) IEEE 802.11, generally an Orthogonal Frequency DivisionMultiple Access (OFDMA) network, a Time Division Multiple Access (TDMA)network, a Code Division Multiple Access (CDMA) network, a Wideband-CDMA(WCDMA) network, a Frequency Division Multiple Access (FDMA) network, aSpatial Division Multiple Access (SDMA) network, etc.

For further illustrating the SAR ADC calibration described above, FIG. 8illustrates a flowchart of a method 800 for calibrating one of the abovedescribed n-bit SAR ADCs. For a first calibration measurement 802, themethod 800 comprises controlling 802-1 the second switch circuits of onehalf of the sampling cells for each bit of the n-bit to couple therespective second cell input to the respective capacitive element, andcontrolling 802-2 the second switch circuits of the other half of thesampling cells for each bit of the n-bit to couple the respective thirdcell input to the respective capacitive element.

For i-th calibration measurements 804 (1<i<n+1), the method 800comprises controlling 804-1 the second switch circuits of the samplingcells for the i−1st most significant bit among the n-bits tosequentially couple the respective second cell input and the respectivethird cell input to the respective capacitive element. Further, if i>2,the method 800 additionally comprises controlling 804-2 the secondswitch circuits of the sampling cells for the bits up to the i−2nd mostsignificant bit to couple a selected one of the respective second cellinput and the respective third cell input to the respective capacitiveelement. For the i-th calibration measurements 804, the method 800comprises controlling 804-3 the second switch circuits of one half ofthe sampling cells for each of the i-th to n-th most significant bits tocouple the respective second cell input to the respective capacitiveelement, and controlling 804-4 the second switch circuits of the otherhalf of the sampling cells for each of the i-th to n-th most significantbits to couple the respective third cell input to the respectivecapacitive element.

For a n+1 st calibration measurement 806, the method 800 comprisescontrolling 806-1 the second switch circuits of the sampling cells forthe bits up to the n−1^(st) most significant bits to couple the selectedone of the respective second cell input and the respective third cellinput to the respective capacitive element, and controlling 806-2 thesecond switch circuits of the sampling cells for the n-th mostsignificant bit to sequentially couple the respective second cell inputand the respective third cell input to the respective capacitiveelement.

The method 800 may allow facilitated calibration of the n-bit SAR ADC.

Optionally, the method 800 may comprise one or more optional featuressuch as, e.g., determining a respective value for the weight of thesampling cells for the i−1^(st) most significant bit based on thecomparison signal for the i-th calibration measurement, determining avalue for the weight of the sampling cells for the n-th most significantbit based on the comparison signal for the n+1st calibrationmeasurement, or selecting the selected one of the respective second cellinput and the respective third cell input based on the comparison signalfor the first calibration measurement.

More details and aspects of the method 800 are explained in connectionwith the proposed technique or one or more examples described above(e.g. FIGS. 1 to 5). The method 800 may comprise one or more additionaloptional features corresponding to one or more aspects of the proposedtechnique or one or more examples described above.

The examples described herein may be summarized as follows:

Example 1 is a n-bit SAR ADC, comprising: a respective plurality ofsampling cells for each bit of the n-bit of the SAR ADC, wherein eachsampling cell comprises: a capacitive element coupled to a cell outputof the sampling cell in order to provide a cell output signal; a firstcell input for receiving a first signal; a first switch circuit capableof selectively coupling the first cell input to the capacitive element;a second cell input for receiving a second signal; a third cell inputfor receiving a third signal, wherein the third signal exhibits oppositepolarity compared to the second signal; and a second switch circuitcapable of selectively coupling one of the second cell input and thethird cell input to the capacitive element; at least one comparatorcircuit coupled to the sampling cells, wherein the at least onecomparator circuit is configured to output a comparison signal based onthe cell output signals of the sampling cells; and a calibration circuitconfigured to supply at least one respective control signal to therespective second switch circuit of the sampling cells for controllingthe second switch circuits.

Example 2 is the n-bit SAR ADC of example 1, wherein, for a firstcalibration measurement, the calibration circuit is configured to:control the second switch circuits of one half of the sampling cells foreach bit of the n-bit to couple the second cell input to the respectivecapacitive element; and control the second switch circuits of the otherhalf of the sampling cells for each bit of the n-bit to couple the thirdcell input to the respective capacitive element.

Example 3 is the n-bit SAR ADC of example 2, wherein, for i-thcalibration measurements with 1<i<n+1, the calibration circuit isconfigured to respectively: control the second switch circuits of thesampling cells for the i−1st most significant bit of the n-bit tosequentially couple the second cell input and the third cell input tothe respective capacitive element; if i>2, control the second switchcircuits of the sampling cells for the bits up to the i−2nd mostsignificant bit to couple a selected one of the second cell input andthe third cell input to the respective capacitive element; control thesecond switch circuits of one half of the sampling cells for each of thei-th to n-th most significant bits to couple the second cell input tothe respective capacitive element; and control the second switchcircuits of the other half of the sampling cells for each of the i-th ton-th most significant bits to couple the third cell input to therespective capacitive element.

Example 4 is the n-bit SAR ADC of example 3, wherein the calibrationcircuit is configured to determine a respective value for the weight ofthe sampling cells for the i−1st most significant bit based on thecomparison signal for the i-th calibration measurement.

Example 5 is the n-bit SAR ADC of example 3 or example 4, wherein, for an+1st calibration measurement, the calibration circuit is configured to:control the second switch circuits of the sampling cells for the bits upto the n−1^(st) most significant bit to couple the selected one of thesecond cell input and the third cell input to the respective capacitiveelement; and control the second switch circuits of the sampling cellsfor the n-th most significant bit to sequentially couple the second cellinput and the third cell input to the respective capacitive element.

Example 6 is the n-bit SAR ADC of example 5, wherein the calibrationcircuit is configured to determine a value for the weight of thesampling cells for the n-th most significant bit based on the comparisonsignal for the n+1st calibration measurement.

Example 7 is the n-bit SAR ADC of any of examples 3 to 6, wherein thecalibration circuit is configured to select the selected one of thesecond cell input and the third cell input based on the comparisonsignal for the first calibration measurement.

Example 8 is the n-bit SAR ADC of any of examples 3 to 7, wherein thefirst cell input of at least one of the sampling cells is a cell inputof the respective sampling cell used for receiving an input signal to bedigitized during non-calibration operation of the n-bit SAR ADC.

Example 9 is the n-bit SAR ADC of any of examples 3 to 7, wherein atleast one of the sampling cells further comprises: a fourth cell inputfor receiving an input signal to be digitized during non-calibrationoperation of the n-bit SAR ADC, and a third switch circuit capable ofselectively coupling the fourth cell input to the capacitive elementbased on a clock signal in order to sample the input signal.

Example 10 is the n-bit SAR ADC of any of examples 3 to 9, wherein thecalibration circuit is configured to selectively control the respectivefirst switch circuit to couple the respective first cell input to thecapacitive element during calibration.

Example 11 is the n-bit SAR ADC of any of examples 1 to 9, wherein eachsampling cell comprises a respective fifth cell input for receiving afourth signal, wherein the fourth signal exhibits opposite polaritycompared to the first signal, and wherein the respective first switchcircuit is capable of selectively coupling one of the respective firstcell input and the respective fifth cell input to the respectivecapacitive element.

Example 12 is the n-bit SAR ADC of example 11, wherein the calibrationcircuit is configured to selectively control the respective first switchcircuit to couple a selected one of the respective first cell input andthe respective fifth cell input to the respective capacitive elementduring calibration.

Example 13 is the n-bit SAR ADC of any of examples 1 to 12, wherein thecapacitive elements of a respective one of the pluralities of samplingcells for the individual bits of the n-bit exhibit the same capacitance.

Example 14 is the n-bit SAR ADC of any of examples 1 to 13, wherein thecapacitive elements of different ones of the pluralities of samplingcells for the individual bits of the n-bit exhibit differentcapacitances.

Example 15 is the n-bit SAR ADC of example 14, wherein the capacitiveelements of a respective one of the pluralities of sampling cells forthe individual bits of the n-bit exhibit a respective capacitance whichcorresponds to the significance of the respective bit.

Example 16 is the n-bit SAR ADC of any of examples 1 to 15, wherein n>1.

Example 17 is the n-bit SAR ADC of any of examples 1 to 16, wherein thefirst signal is a calibration signal, wherein the second signal is afirst reference signal, and wherein the third signal is a secondreference signal.

Example 18 is the n-bit SAR ADC of any of examples 1 to 17, wherein thecalibration circuit is configured to supply the respective controlsignal the respective second switch circuit of the sampling cells inorder to adjust a decision threshold for the at least one comparatorcircuit during calibration.

Example 19 is a receiver, comprising: an n-bit SAR ADC according to anyof examples 1 to 18; and a signal generation circuit configured togenerate the first signal.

Example 20 is the receiver of example 19, wherein the first signalexhibits an increasing or decreasing signal level.

Example 21 is a base station, comprising: a receiver according toexample 19 or example 20; and at least one antenna element coupled tothe receiver.

Example 22 is the base station of example 21, further comprising atransmitter configured to supply a radio frequency transmit signal tothe antenna element for radiation to the environment.

Example 23 is a mobile device, comprising: a receiver according toexample 19 or example 20; and at least one antenna element coupled tothe receiver.

Example 24 is the mobile device of example 23, further comprising atransmitter configured to supply a radio frequency transmit signal tothe antenna element for radiation to the environment.

Example 25 is a method for calibrating the n-bit SAR ADC according toany of examples 1 to 18, the method comprising: for a first calibrationmeasurement: controlling the second switch circuits of one half of thesampling cells for each bit of the n-bit to couple the second cell inputto the respective capacitive element; and controlling the second switchcircuits of the other half of the sampling cells for each bit of then-bit to couple the third cell input to the respective capacitiveelement, for i-th calibration measurements with 1<i<n+1: controlling thesecond switch circuits of the sampling cells for the i−1^(st) mostsignificant bit among the n-bits to sequentially couple the second cellinput and the third cell input to the respective capacitive element; ifi>2, controlling the second switch circuits of the sampling cells forthe bits up to the i−2nd most significant bit to couple a selected oneof the second cell input and the third cell input to the respectivecapacitive element; controlling the second switch circuits of one halfof the sampling cells for each of the i-th to n-th most significant bitsto couple the second cell input to the respective capacitive element;and controlling the second switch circuits of the other half of thesampling cells for each of the i-th to n-th most significant bits tocouple the third cell input to the respective capacitive element, andfor a n+1st calibration measurement: controlling the second switchcircuits of the sampling cells for the bits up to the n−1^(st) mostsignificant bit to couple the selected one of the second cell input andthe third cell input to the respective capacitive element; andcontrolling the second switch circuits of the sampling cells for then-th most significant bit to sequentially couple the second cell inputand the third cell input to the respective capacitive element.

Example 26 is the method of example 25, further comprising: determininga respective value for the weight of the sampling cells for the i−1^(st)most significant bit based on the comparison signal for the i-thcalibration measurement.

Example 27 is the method of example 25 or example 26, furthercomprising: determining a value for the weight of the sampling cells forthe n-th most significant bit based on the comparison signal for then+1st calibration measurement.

Example 28 is the method of any of examples 25 to 27, furthercomprising: selecting the selected one of the second cell input and thethird cell input based on the comparison signal for the firstcalibration measurement.

Example 29 is the method of any of examples 25 to 28, wherein the firstsignal exhibits an increasing or decreasing signal level.

The aspects and features mentioned and described together with one ormore of the previously detailed examples and figures, may as well becombined with one or more of the other examples in order to replace alike feature of the other example or in order to additionally introducethe feature to the other example.

Examples may further be or relate to a computer program having a programcode for performing one or more of the above methods, when the computerprogram is executed on a computer or processor. Steps, operations orprocesses of various above-described methods may be performed byprogrammed computers or processors. Examples may also cover programstorage devices such as digital data storage media, which are machine,processor or computer readable and encode machine-executable,processor-executable or computer-executable programs of instructions.The instructions perform or cause performing some or all of the acts ofthe above-described methods. The program storage devices may comprise orbe, for instance, digital memories, magnetic storage media such asmagnetic disks and magnetic tapes, hard drives, or optically readabledigital data storage media. Further examples may also cover computers,processors or control units programmed to perform the acts of theabove-described methods or (field) programmable logic arrays ((F)PLAs)or (field) programmable gate arrays ((F)PGAs), programmed to perform theacts of the above-described methods.

The description and drawings merely illustrate the principles of thedisclosure. Furthermore, all examples recited herein are principallyintended expressly to be only for illustrative purposes to aid thereader in understanding the principles of the disclosure and theconcepts contributed by the inventor(s) to furthering the art. Allstatements herein reciting principles, aspects, and examples of thedisclosure, as well as specific examples thereof, are intended toencompass equivalents thereof.

A functional block denoted as “means for . . . ” performing a certainfunction may refer to a circuit that is configured to perform a certainfunction. Hence, a “means for s.th.” may be implemented as a “meansconfigured to or suited for s.th.”, such as a device or a circuitconfigured to or suited for the respective task.

Functions of various elements shown in the figures, including anyfunctional blocks labeled as “means”, “means for providing a signal”,“means for generating a signal.”, etc., may be implemented in the formof dedicated hardware, such as “a signal provider”, “a signal processingunit”, “a processor”, “a controller”, etc. as well as hardware capableof executing software in association with appropriate software. Whenprovided by a processor, the functions may be provided by a singlededicated processor, by a single shared processor, or by a plurality ofindividual processors, some of which or all of which may be shared.However, the term “processor” or “controller” is by far not limited tohardware exclusively capable of executing software, but may includedigital signal processor (DSP) hardware, network processor, applicationspecific integrated circuit (ASIC), field programmable gate array(FPGA), read only memory (ROM) for storing software, random accessmemory (RAM), and nonvolatile storage. Other hardware, conventionaland/or custom, may also be included.

A block diagram may, for instance, illustrate a high-level circuitdiagram implementing the principles of the disclosure. Similarly, a flowchart, a flow diagram, a state transition diagram, a pseudo code, andthe like may represent various processes, operations or steps, whichmay, for instance, be substantially represented in computer readablemedium and so executed by a computer or processor, whether or not suchcomputer or processor is explicitly shown. Methods disclosed in thespecification or in the claims may be implemented by a device havingmeans for performing each of the respective acts of these methods.

It is to be understood that the disclosure of multiple acts, processes,operations, steps or functions disclosed in the specification or claimsmay not be construed as to be within the specific order, unlessexplicitly or implicitly stated otherwise, for instance for technicalreasons. Therefore, the disclosure of multiple acts or functions willnot limit these to a particular order unless such acts or functions arenot interchangeable for technical reasons. Furthermore, in some examplesa single act, function, process, operation or step may include or may bebroken into multiple sub-acts, -functions, -processes, -operations or-steps, respectively. Such sub acts may be included and part of thedisclosure of this single act unless explicitly excluded.

Furthermore, the following claims are hereby incorporated into thedetailed description, where each claim may stand on its own as aseparate example. While each claim may stand on its own as a separateexample, it is to be noted that—although a dependent claim may refer inthe claims to a specific combination with one or more other claims—otherexamples may also include a combination of the dependent claim with thesubject matter of each other dependent or independent claim. Suchcombinations are explicitly proposed herein unless it is stated that aspecific combination is not intended. Furthermore, it is intended toinclude also features of a claim to any other independent claim even ifthis claim is not directly made dependent to the independent claim.

What is claimed is:
 1. A n-bit Successive Approximation RegisterAnalog-to-Digital Converter, SAR ADC, comprising: a respective pluralityof sampling cells for each bit of the n-bit of the SAR ADC, wherein eachsampling cell comprises: a capacitive element coupled to a cell outputof the sampling cell in order to provide a cell output signal; a firstcell input for receiving a first signal; a first switch circuit capableof selectively coupling the first cell input to the capacitive element;a second cell input for receiving a second signal; a third cell inputfor receiving a third signal, wherein the third signal exhibits oppositepolarity compared to the second signal; and a second switch circuitcapable of selectively coupling one of the second cell input and thethird cell input to the capacitive element; at least one comparatorcircuit coupled to the sampling cells, wherein the at least onecomparator circuit is configured to output a comparison signal based onthe cell output signals of the sampling cells; and a calibration circuitconfigured to supply at least one respective control signal to therespective second switch circuit of the sampling cells for controllingthe second switch circuits.
 2. The n-bit SAR ADC of claim 1, wherein,for a first calibration measurement, the calibration circuit isconfigured to: control the second switch circuits of one half of thesampling cells for each bit of the n-bit to couple the second cell inputto the respective capacitive element; and control the second switchcircuits of the other half of the sampling cells for each bit of then-bit to couple the third cell input to the respective capacitiveelement.
 3. The n-bit SAR ADC of claim 2, wherein, for i-th calibrationmeasurements with 1<i<n+1, the calibration circuit is configured torespectively: control the second switch circuits of the sampling cellsfor the i−1st most significant bit of the n-bit to sequentially couplethe second cell input and the third cell input to the respectivecapacitive element; if i>2, control the second switch circuits of thesampling cells for the bits up to the i−2nd most significant bit tocouple a selected one of the second cell input and the third cell inputto the respective capacitive element; control the second switch circuitsof one half of the sampling cells for each of the i-th to n-th mostsignificant bits to couple the second cell input to the respectivecapacitive element; and control the second switch circuits of the otherhalf of the sampling cells for each of the i-th to n-th most significantbits to couple the third cell input to the respective capacitiveelement.
 4. The n-bit SAR ADC of claim 3, wherein the calibrationcircuit is configured to determine a respective value for the weight ofthe sampling cells for the i−1st most significant bit based on thecomparison signal for the i-th calibration measurement.
 5. The n-bit SARADC of claim 3, wherein, for a n+1st calibration measurement, thecalibration circuit is configured to: control the second switch circuitsof the sampling cells for the bits up to the n−1^(st) most significantbit to couple the selected one of the second cell input and the thirdcell input to the respective capacitive element; and control the secondswitch circuits of the sampling cells for the n-th most significant bitto sequentially couple the second cell input and the third cell input tothe respective capacitive element.
 6. The n-bit SAR ADC of claim 5,wherein the calibration circuit is configured to determine a value forthe weight of the sampling cells for the n-th most significant bit basedon the comparison signal for the n+1st calibration measurement.
 7. Then-bit SAR ADC of claim 3, wherein the calibration circuit is configuredto select the selected one of the second cell input and the third cellinput based on the comparison signal for the first calibrationmeasurement.
 8. The n-bit SAR ADC of claim 3, wherein the first cellinput of at least one of the sampling cells is a cell input of therespective sampling cell used for receiving an input signal to bedigitized during non-calibration operation of the n-bit SAR ADC.
 9. Then-bit SAR ADC of claim 3, wherein at least one of the sampling cellsfurther comprises: a fourth cell input for receiving an input signal tobe digitized during non-calibration operation of the n-bit SAR ADC, anda third switch circuit capable of selectively coupling the fourth cellinput to the capacitive element based on a clock signal in order tosample the input signal.
 10. The n-bit SAR ADC of claim 3, wherein thecalibration circuit is configured to selectively control the respectivefirst switch circuit to couple the respective first cell input to thecapacitive element during calibration.
 11. The n-bit SAR ADC of claim 1,wherein each sampling cell comprises a respective fifth cell input forreceiving a fourth signal, wherein the fourth signal exhibits oppositepolarity compared to the first signal, and wherein the respective firstswitch circuit is capable of selectively coupling one of the respectivefirst cell input and the respective fifth cell input to the respectivecapacitive element.
 12. The n-bit SAR ADC of claim 11, wherein thecalibration circuit is configured to selectively control the respectivefirst switch circuit to couple a selected one of the respective firstcell input and the respective fifth cell input to the respectivecapacitive element during calibration.
 13. The n-bit SAR ADC of claim 1,wherein the capacitive elements of a respective one of the pluralitiesof sampling cells for the individual bits of the n-bit exhibit the samecapacitance.
 14. The n-bit SAR ADC of claim 1, wherein the capacitiveelements of different ones of the pluralities of sampling cells for theindividual bits of the n-bit exhibit different capacitances.
 15. Then-bit SAR ADC of claim 14, wherein the capacitive elements of arespective one of the pluralities of sampling cells for the individualbits of the n-bit exhibit a respective capacitance which corresponds tothe significance of the respective bit.
 16. The n-bit SAR ADC of claim1, wherein n>1.
 17. The n-bit SAR ADC of claim 1, wherein the firstsignal is a calibration signal, wherein the second signal is a firstreference signal, and wherein the third signal is a second referencesignal.
 18. The n-bit SAR ADC of claim 1, wherein the calibrationcircuit is configured to supply the respective control signal therespective second switch circuit of the sampling cells in order toadjust a decision threshold for the at least one comparator circuitduring calibration.
 19. A receiver, comprising: an n-bit successiveapproximation register analog-to-digital converter according to claim 1;and a signal generation circuit configured to generate the first signal.20. The receiver of claim 19, wherein the first signal exhibits anincreasing or decreasing signal level.
 21. A base station, comprising: areceiver according to claim 19; and at least one antenna element coupledto the receiver.
 22. The base station of claim 21, further comprising atransmitter configured to supply a radio frequency transmit signal tothe antenna element for radiation to the environment.
 23. A method forcalibrating the n-bit SAR ADC according to claim 1, the methodcomprising: for a first calibration measurement: controlling the secondswitch circuits of one half of the sampling cells for each bit of then-bit to couple the second cell input to the respective capacitiveelement; and controlling the second switch circuits of the other half ofthe sampling cells for each bit of the n-bit to couple the third cellinput to the respective capacitive element, for i-th calibrationmeasurements with 1<i<n+1: controlling the second switch circuits of thesampling cells for the i−1^(st) most significant bit among the n-bits tosequentially couple the second cell input and the third cell input tothe respective capacitive element; if i>2, controlling the second switchcircuits of the sampling cells for the bits up to the i−2nd mostsignificant bit to couple a selected one of the second cell input andthe third cell input to the respective capacitive element; controllingthe second switch circuits of one half of the sampling cells for each ofthe i-th to n-th most significant bits to couple the second cell inputto the respective capacitive element; and controlling the second switchcircuits of the other half of the sampling cells for each of the i-th ton-th most significant bits to couple the third cell input to therespective capacitive element, and for a n+1^(st) calibrationmeasurement: controlling the second switch circuits of the samplingcells for the bits up to the n−1^(st) most significant bit to couple theselected one of the second cell input and the third cell input to therespective capacitive element; and controlling the second switchcircuits of the sampling cells for the n-th most significant bit tosequentially couple the second cell input and the third cell input tothe respective capacitive element.
 24. The method of claim 23, furthercomprising: determining a respective value for the weight of thesampling cells for the i−1^(st) most significant bit based on thecomparison signal for the i-th calibration measurement.
 25. The methodof claim 24, further comprising: determining a value for the weight ofthe sampling cells for the n-th most significant bit based on thecomparison signal for the n+1st calibration measurement.